There are cases where it is desired to cut a groove in a three-dimensional curved surface.
FIG. 6 is a view for describing a prior-art example of such grooving machining. SS denotes a three-dimensional curved surface, GR a groove, and Mk (k=1, 2, . . . ) a series of points on the three-dimensional curved surface specifying the groove GR. Grooving machining entails obtaining the coordinates of the series of points Mk specifying the groove GR, subsequently obtaining the coordinates of a series of points lower than the abovementioned coordinates by the dimension h of groove depth along the -Z axis, creating NC data based on these coordinates, and cutting the groove based on the NC data.
In the prior art, the groove depth dimension h is fixed at all times. Consequently, the coordinates of the series of points on the groove bottom can be obtained automatically and the NC data for grooving can be created with ease. However, if the groove depth dimension h varies, the coordinates of the series of points on the groove bottom cannot be found automatically but must be calculated manually by the operator. Accordingly, creating NC data for cutting a groove having a varying depth is a troublesome task.